Apparatus for the diameter checking of eccentric portions of a mechanical piece in the course of the machining in a grinding machine

ABSTRACT

An apparatus ( 10 ) for checking the diameter of an eccentric pin ( 8 ′) of a small-size shaft ( 8 ), for example a shaft for compressors, includes a support ( 16 ), a first arm ( 19 ) rotating with respect to the support ( 16 ), a second arm ( 22 ) rotating with respect to the first, a Vee-shaped reference device ( 28 ) carried by the second arm, a measuring device ( 25,26,24,37,38 ) associated with the reference device, limiting devices ( 29,29′,30,30′ ) for limiting the rotations of the arms and thrust means ( 33 ) for keeping the reference device in contact with the pin in the course of the checking. A hydraulic actuator ( 13 ) displaces the apparatus ( 10 ) from a rest condition to a checking condition, in which the reference device ( 28 ) is in contact with the pin ( 8 ′) to be checked, and vice versa.

TECHNICAL FIELD

The present invention relates to an apparatus for the diameter checkingof a substantially cylindrical eccentric portion of a mechanical piecethat defines a geometrical axis, during eccentric rotations of saidportion about the geometrical axis, including a substantially Vee-shapedreference device, adapted for cooperating with the eccentric portion tobe checked, a measuring device, movable with the reference device, and asupport device for supporting the reference device and the measuringdevice, the support device including a support element, a firstrotating, coupling element coupled to the support element so as torotate about an axis of rotation parallel to the geometrical axis, asecond rotating, coupling element that carries the reference device andthe measuring device and is coupled to the first coupling element so asto rotate relative to it about an additional axis of rotation parallelto the geometrical axis and to the axis of rotation, and limiting andreference devices, for limiting the rotations of the first rotating,coupling element and the second rotating, coupling element and fordefining a rest condition of the apparatus without interfering withdisplacements of the reference device following the substantiallycylindrical portion during said eccentric rotations.

BACKGROUND ART

There are known apparatuses with these characteristics for the checkingof pins rotating with orbital motion in the course of the machining in agrinding machine. For example, international patent applicationpublished with No. WO-A-9712724, filed by the same applicant of thepresent patent application, discloses an apparatus for the checking ofthe diameter of crankpins in orbital motion in the course of themachining of crankshafts in a grinding machine including a bed, aworktable, a grinding-wheel slide and a grinding wheel coupled to thegrinding-wheel slide. The apparatus is coupled to the grinding-wheelslide, contacts the piece and follows it in the course of its orbitalmotion substantially by virtue of the force of gravity applied to theconsiderable mass of the apparatus. The apparatus is particularlysuitable for checking crankshafts for automobile engines and hasappropriate mass and layout dimensions.

Owing to the considerable layout dimensions, apparatuses of this typecannot be coupled to the grinding-wheel slide of small-size grindingmachines, as those utilized for the machining of shafts for compressors,like the one (8) shown in FIG. 1, more particularly its associatedeccentric pin 8′. The dimensions of these shafts are by far smaller thanthose of the crankshafts: a shaft for compressors is typically 150-200mm long and the eccentric pin is approximately 12-40 mm in diameter,while a crankshaft measures at least 50-100 cm in length and thediameter of a crankpin may range, for example, within 40 to 90 mm. Inorder to carry out the diameter checking, during the machining of theseeccentric pins, the presently utilized applications are substantiallysimilar to the one illustrated and described in italian patent No.1258154. These applications (an example is shown in simplified form inFIG. 2) include two stationary gauging or measuring heads H1 and H2,coupled to the machine bed B or to the worktable, with feelers forcontacting the pin, in the course of its eccentric rotation, just at twodiametrally opposite points, P1 and P2, of its trajectory T. Thediameter of the pin is calculated by evaluating information relating tothe position of said two points of the trajectory and carrying outappropriate processings that keep into account the geometry of thechecked piece.

Even though the utilization of a checking application of this type issimple, it cannot guarantee satisfactory metrological performancesbecause, among other things, the diameter of the pin is “deduced” on thebasis of checkings carried out by touching the same point of the surfacein two opposite arrangements of the piece.

It is not possible to determine whether any possible variations detectedby either of the two heads is due to diameter variations, to shapeand/or eccentricity errors or to a combination of such factors.Furthermore, the measurement combining the detections of the two headsis also affected by the mutual arrangement existing between the heads,and by possible modifications of said arrangement. Furthermore, thedetecting and processing operation is slow and, whenever the nominaldiameter dimensions of the piece to be checked vary, it is necessary tomanually reset the application and consequently this implies machinedown-time and considerable loss of time.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an apparatus forchecking eccentric pins of small-size shafts, while the pinseccentrically rotate in the course of the machining in a grindingmachine, that overcomes the drawbacks of the known apparatuses andprovides good metrological performance and high standards of reliabilityand flexibility.

This and other objects are attained by an apparatus according to claim1.

An apparatus according to the invention provides the advantage of beingable to follow the piece, eccentrically rotating at high speeds (in theorder of some hundreds of revolutions per minute), thanks to its limitedmass and to the traction force of the spring, as hereinafter disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described in more detail with reference to theenclosed sheets of drawings, given by way of non-limiting example,wherein:

FIG. 1 shows a shaft for compressors;

FIG. 2 is a lateral view, shown in simplified form, of a known measuringapparatus for the checking of the diameter of eccentric pins of a shaftfor compressors, in the course of the machining in a grinding machine;

FIG. 3 is a side view of a measuring apparatus according to theinvention, mounted on the bed of a grinding machine for grindingeccentric pins of shafts for compressors;

FIG. 4 is an enlarged and partly cross-sectional view of the apparatusshown in FIG. 3, according to a different operating position;

FIG. 5 is a cross-sectional view of the measuring apparatus shown inFIG. 4, in a different scale and according to different planes,identified by line V—V in FIG. 4;

FIG. 6 shows a component part, in a different scale, of the measuringdevice of the apparatus shown in FIG. 4; and

FIG. 7 is a side view of a measuring apparatus according to a differentembodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 3, a computer numerical control (“CNC”) grindingmachine 1 includes a bed 2, to which there is coupled a grinding-wheelslide 3, for supporting a spindle 4, that defines the axis of rotation 5of the grinding wheel 6. The grinding-wheel slide 3 can displacerelative to bed 2 in a known way as indicated in FIG. 3 by arrow F.

A worktable 7, carrying the piece to be checked—for example a shaft 8for compressors with at least a cylindrical eccentric portion, or pin,8′—is coupled to bed 2 between a spindle and a tailstock, not shown,that define the axis of rotation 9, coincident with the main geometricalaxis of piece 8. Consequently, in the course of the rotation of piece 8,crankpin 8′ performs an eccentric motion about axis 9.

Moreover, there is coupled to bed 2 an apparatus 10—also shown in FIGS.4 and 5—for checking, during the machining, the diametral dimensionsand/or possible shape errors of pin 8′ of piece 8. The apparatus 10 iscoupled to a slide 12, that can displace in a transversal direction andis activated by a hydraulic actuator 13 including a cylinder 14 and apiston 15. Cylinder 14 of the hydraulic actuator 13 is coupled to bed 2by means of a support 11, while piston 15 carries slide 12. Theapparatus 10 includes a support element 16 coupled to slide 12 and, bymeans of a rotation pin 17—that defines a first axis of rotation 18,parallel to the axis of rotation 5 of grinding wheel 6 and to the axisof rotation 9 of piece 8—it supports a first rotating, coupling element19. In turn, coupling element 19, by means of a rotation pin 20—thatdefines a second axis of rotation 21 parallel to the axis of rotation 5of grinding wheel 6 and to the axis of rotation 9 of piece 8—supports asecond rotating, coupling element 22.

A measuring device includes a tubular guide casing 24 coupled by meansof screws, at an enlarged portion 31, to coupling element 22. Withintubular guide casing 24 there is a transmission rod 25, shown in FIG. 6,that can axially translate and carries a feeler 26, for contacting thesurface of pin 8′ of piece 8 to be checked.

The free end of the tubular guide casing 24 is coupled to a supportblock 27 for supporting a reference device 28, in the shape of a Vee,for engaging with the surface of pin 8′ of piece 8 to be checked, byvirtue of the rotations enabled by pins 17 and 20. The transmission rod25 is movable along the bisecting line of the Vee-shaped referencedevice 28.

Limiting and reference devices, shown in FIG. 3 and partially in FIG. 4,include a first and a second pair of abutment surfaces. The first paircomprises a surface 29 of the rotating, coupling element 19 and asurface of a corresponding abutment element, more specifically a dowel30 coupled in an adjustable way to a stanchion 23 integral with thesupport element 16. The second pair of abutment surfaces includes asurface 29′ of a block 29″ coupled to the second rotating, couplingelement 22 and a surface of a corresponding abutment element, morespecifically a dowel 30′ coupled in an adjustable way to a plate 23′integral with the support element 16. The rotations of the couplingelement 19 about the axis of rotation 18 are limited, in a clockwisedirection (with reference to FIGS. 3 and 4), by contact occurringbetween the abutment surface 29 and the dowel 30, whereas rotations ofthe coupling element 22 are limited, in a clockwise direction (FIGS. 3and 4), by contact occurring between the abutment surface 29′ and dowel30′. The position of dowels 30 and 30′ can be adjusted, as previouslymentioned, for the purpose of modifying the amount of the rotations ofthe first coupling element 19 and the second coupling element 22.

A thrust device includes a return spring 33, with its ends coupled to afirst support element 34, clamped to the first coupling element 19 bymeans of the head 32 of a screw, and integrally rotating together withit about axis 18, and to the end of a screw 35, screwed to a secondsupport element 34′ fixed to the support element 16.

The previously mentioned return spring 33 keeps in rest conditions, theabutment surface 29 of the coupling element 19 in abutment with dowel30, and, in the course of the checking, urges the reference device 28against the surface of pin 8′ of the piece 8 keeping feeler 26 incontact with such surface of the pin 8′. It is possible to decrease orincrease the traction force of spring 33 by screwing or unscrewing,respectively, screw 35 and then operating a nut 35′ for locking saidscrew 35 in the required position.

In rest conditions, in other words when there is no piece 8 to bechecked on worktable 7, the position of the coupling elements 19 and 22is defined by the abutment between surface 29 and dowel 30—urged againsteach other by the thrust of spring 33—and, respectively, by contactbetween surface 29′ and dowel 30′; this contact is determined by theforce of gravity that acts on element 22 and the measuring devicecoupled to it. In said rest condition, hydraulic actuator 13 maintainsslide 12 in a retracted position according to which the Vee-shapedreference device 28 is far from worktable 7.

Then piece 8 is positioned on worktable 7, between the spindle and thetailstock. Consequently, pin 8′ undergoes an eccentric rotation aboutaxis 9. In FIG. 3 a dashed line indicates the trajectory 36 of axis 9′of pin 8′, also shown in FIG. 1, in the course of its eccentricrotation. Before piece 8 starts to rotate, the hydraulic actuator 13displaces slide 12 to a checking position according to which surfaces ofthe reference device 28 contact the surface of pin 8′.

It should be realized that reference device 28 can be displaced towardspiece 8 while the latter is in rotation. Regardless of whether the pieceis stationary or moving, it is in any case possible to rapidly achievecorrect cooperation between pin 8′ and reference device 28.

Thanks to spring 33, reference device 28 maintains contact with pin 8′during the motion of piece 8, thus following it in its eccentricrotation.

Subsequently to the arrangement of the Vee 28 on the pin 8′, thesurfaces 29 and 29′ get detached from their associated dowels 30, 30′and, by virtue of the appropriate position undertaken by dowels 30, 30′and by slide 12, the limiting and reference means do not interfere withthe displacements of the reference device 28 following the pin 8′.

The return of the checking apparatus 10 to the rest condition, effectedby the hydraulic actuator, is normally controlled by the grindingmachine numerical control when, on the basis of the measurement signaldetected and transmitted by the checking apparatus, it is detected thatpin 8′ has reached the required (diameter) dimension. This return iseffected by means of an extension of piston 15 of hydraulic actuator 13,causing the reference device 28 to move away from the surface of pin 8′and the surfaces 29 and 29′ to contact their associated dowels 30 and30′ again. Then the machining of another pin 8′ takes place, or—if themachining of piece 8 has ended—piece 8 is unloaded, manually orautomatically, and another piece 8 is loaded on worktable 7.

In the event the piece, unlike the one shown in FIG. 1, has a pluralityof eccentric pins and there be the need to machine a fresh pin 8′, thelatter is carried in front of grinding wheel 6, typically by displacingworktable 7 (in the case of a grinding machine with a single grindingwheel), and the checking apparatus 10 is moved to the operatingposition.

FIG. 6 shows in more detail some elements of the measuring device ofapparatus 10.

The axial displacements of the transmission rod 25 relative to areference position are detected by a measurement transducer 37, of theknown type, coupled to the tubular casing 24 and with a magnetic corecoupled to a stem 38 screwed to the transmission rod 25.

The axial displacement of the transmission rod 25 is guided by twobushings 40, 40′ arranged between casing 24 and rod 25. A metal bellows41, that is stiff with respect to torsional forces and has its endsfixed to rod 25 and casing 24, respectively, accomplishes the dualfunction of preventing rod 25 from rotating with respect to casing 24(thus preventing feeler 26 from taking improper positions) and sealingthe lower end of casing 24.

The reference device 28 consists of two elements 45 and 46 with slantingside surfaces, whereto there are secured two bars 47 and 48.

The coupling between support block 27 and reference device 28 isprovided by screws 43 traversing slots 44 and enables axial mutualadjustments, substantially along the direction of the bisecting line ofthe Vee defined by bars 47 and 48, for ensuring contact of the two bars47 and 48 and that of feeler 26 with pin 8′ of piece 8.

Each reference device 28 features particular dimensions and geometry(e.g. the Vee angle) allowing to cover a specific measuring range. Whenthe latter varies, it is possible to replace the reference device withanother one featuring a different layout by carrying out simple andrapid operations.

Even feeler 26 can be replaced in an equally rapid and simple waywhenever it is required to do so by the specific application.

The apparatus shown in FIG. 7 is substantially similar to the one ofFIGS. 3 to 6, and features a detecting device 50, for detecting theangular position of pin 8′ about axis 9. The detecting device 50comprises a linear gauge, e.g. a so-called “cartridge head” 51,including an axially movable feeler 52 and a transducer—well-known andnot shown in the figure—that provides signals indicative of thedisplacements of feeler 52. A protruding element or stud 53 isintegrally coupled to the first coupling element 19, and moves with it,substantially tracing an arc about axis 18. The head 51 is connected tothe slide 12—and consequently to the support element 16—in a properposition (e.g. by means of a bracket, as shown in FIG. 7) allowing thefeeler 52 and the stud 53 to intermittently come in touch with eachother in the course of the checking of eccentrically rotating pin 8′. Inparticular, the contact between feeler 52 and stud 53 takes place atangular positions of pin 8′ about the position shown in FIG. 7. Thesignal provided by head 51, gives indications about arrangements of thefirst coupling element 19 with respect to the support element 16, andallows to detect when pin 8′ assumes the position of FIG. 7, (e.g. ithappens when the signal of head 51 reaches a maximum or minimum value).In such a way, the angular position of pin 81 during its eccentricrotation about axis 9 can be detected.

According to alternative embodiments not shown in the drawings, thedetecting device 50 can include linear gauges 51 differently arrangedwith respect to what is shown in FIG. 7. For instance, the linear gauge51 can be vertically arranged, and include a bar shaped feeler holdingcontinuous contact with stud 53 during the checking cycle of pin 8′ andmoving along a transversal direction with respect to the arc traced bystud 53. In this case too, by monitoring the signal provided by gauge51, it is possible to detect the angular arrangement of pin 8′ about theaxis of rotation 9.

The apparatus is particularly suitable for the checking of the diameterof eccentrically rotating cylindrical portions of mechanical pieces, butit can be generally utilized for the checking of diameters of pieceswith rotational symmetry while rotating eccentrically or about theirgeometrical axes. Even rotating parts having grooved surfaces can bechecked, by choosing a proper reference device 28 and a feeler 26 havinga suitable contact surface (e.g. planar), different with respect to theone that is shown in the drawings.

An apparatus according to the invention enables to obtain remarkablemetrological performance as, unlike what occurs in the knownapplications for eccentrically rotating parts (FIG. 2), the checking ofthe piece takes place during all the phases of the machining.Furthermore, this enables to detect, instant by instant and withoutdelay, the dimensions of pins 8′, thus allowing to retrofit the machinecycle by adjusting some machining parameters.

Lastly, the apparatus according to the invention enables to check thediameter of pieces with nominal dimensions that differ within a specificrange (typically 25 mm), without there being the need to substitute ordisplace any component parts. In this way it is possible to machine andcheck, without stopping the machine, pieces that, although belonging tothe same family, have different nominal dimensions among each other.

Variants with respect to what has been herein described are feasible andmore specifically the checking apparatus can be equipped with additionalfeelers, associated transmission rods and measurement transducers fordetecting additional diameters and other dimensions and/or geometricalor shape features of the pin 8′ being machined. It is obvious that in amulti-wheel grinding machine for simultaneously machining a plurality ofpins 8′ there can be foreseen as many checking apparatuses 10.

An apparatus according to the present invention can be utilized, apartfrom carrying out checkings in the course of the machining as hereindescribed, also for carrying out checkings of the pieces before or afterthe machining.

In an apparatus according to the present invention, feeler 26 can alsotranslate along a direction slightly sloping with respect to thebisecting line of the Vee of the reference device 28, in order toincrease the apparatus sensitivity when performing certain types ofcheckings (e.g. roundness checkings). In the event the machine layoutdimensions do not enable the coupling of the apparatus in a way wherebythe measuring device displaces horizontally, according to the preferredconfiguration shown in the figures, it is possible to couple theapparatus to the machine so that the measuring device arranges itselfalong directions differing from the horizontal one, according to otherconfigurations which guarantee the resting, in rest conditions, of thesurface 29′ on dowel 30′ owing to the force of gravity, or thanks to theaction of an additional spring.

1. An apparatus for the diameter checking of a substantially cylindricaleccentric portion of a mechanical piece that defines a geometrical axis,during eccentric rotations of said portion about said geometrical axis,including a substantially Vee-shaped reference device adapted forcooperating with said eccentric portion to be checked, a measuringdevice, movable with the substantially Vee-shaped reference device, anda support device for supporting the substantially Vee-shaped referencedevice and the measuring device, the support device including a supportelement, a first rotating, coupling element coupled to the supportelement so as to rotate about an axis of rotation parallel to saidgeometrical axis, a second rotating, coupling element that carries thesubstantially Vee-shaped reference device and the measuring device andis coupled to the first coupling element so as to rotate relative to itabout an additional axis of rotation parallel to said geometrical axisand to said axis of rotation, limiting and reference devices with afirst pair and a second pair of abutment surfaces urged to cooperatewith each other for limiting the rotations of said first rotating,coupling element and said second rotating, coupling element and fordefining a rest condition of the apparatus without interfering withdisplacements of the substantially Vee-shaped reference device followingthe substantially cylindrical portion during said eccentric rotations,and a thrust device for urging said substantially Vee-shaped referencedevice in abutment with the cylindrical eccentric portion to be checkedand keeping the substantially Vee-shaped reference device engaged withthe cylindrical eccentric portion during said eccentric rotations, thethrust device being arranged between the support element and one of saidfirst and second coupling elements, the abutment surfaces of said firstpair and second pair being arranged so that they get detached from eachother when the substantially Vee-shaped reference device cooperates withthe eccentric portion to be checked.
 2. The apparatus according to claim1, wherein the abutment surfaces of said first pair are urged tocooperate with each other by the thrust of the thrust device, and theabutment surfaces of said second pair are urged to cooperate with eachother by the force of gravity.
 3. An apparatus for the diameter checkingof a substantially cylindrical eccentric portion of a mechanical piecethat defines a geometrical axis, during eccentric rotations of saidportion about said geometrical axis, including a substantiallyVee-shaped reference device adapted for cooperating with said eccentricportion to be checked, a measuring device, movable with thesubstantially Vee-shaped reference device, and a support device forsupporting the substantially Vee-shaped reference device and themeasuring device, the support device including a support element, afirst rotating, coupling element coupled to the support element so as torotate about an axis of rotation parallel to said geometrical axis, asecond rotating, coupling element that carries the substantiallyVee-shaped reference device and the measuring device and is coupled tothe first coupling element so as to rotate relative to it about anadditional axis of rotation parallel to said geometrical axis and tosaid axis of rotation, limiting and reference device with a first pairand a second pair of abutment surfaces urged to cooperate with eachother for limiting the rotations of said first rotating, couplingelement and said second rotating, coupling element and for defining arest condition of the apparatus without interfering with displacementsof the substantially Vee-shaped reference device following thesubstantially cylindrical portion during said eccentric rotations, and athrust device for urging said substantially Vee-shaped reference devicein abutment with the cylindrical eccentric portion to be checked andkeeping the substantially Vee-shaped reference device engaged with thecylindrical eccentric portion during said eccentric rotations, thethrust device being arranged between the support element and one of saidfirst and second coupling elements, the abutment surfaces of said firstpair and second pair are detached from each other during the checking ofthe eccentric portion, wherein said first pair of abutment surfacesincludes surfaces integral with the support element and with the firstcoupling element that are urged to cooperate with each other by thethrust of the thrust device, and said second pair of abutment surfacesincludes surfaces integral with the support element and the secondcoupling element, the abutment surfaces of the second pair being urgedto cooperate with each other by the force of gravity applied to thesecond coupling element, the substantially Vee-shaped reference deviceand the measuring device.
 4. The apparatus according to claim 3, whereinsaid limiting and reference devices include dowels that define surfacesof said first and second pair of abutment surfaces, the dowels beingcoupled, in an adjustable way, to a stanchion and to a plate,respectively, the stanchion and the plate being coupled to the supportelement.
 5. The apparatus according to claim 1, wherein said thrustdevice includes a return spring coupled to said first coupling elementand said support element.
 6. The apparatus according to claim 1, forchecking the diameter of said substantially cylindrical portioneccentrically rotating about the geometrical axis in the course ofmachining in a numerical control grinding machine with a bed, aworktable, for defining said geometrical axis, and a grindingwheel-slide, movable along a direction, transverse with respect to saidgeometrical axis, wherein said support element is movable with respectto the bed along a direction transverse to the geometrical axis.
 7. Theapparatus according to claim 6, wherein said support element is coupledto a slide, movable with respect to the bed, by means of a hydraulicactuator, said actuator including a cylinder and a piston, said pistonbeing coupled to the slide, and said cylinder being coupled to the bed.8. The apparatus according to claim 1, wherein the measuring deviceincludes a transmission rod and a feeler, coupled to the transmissionrod, adapted for contacting said substantially cylindrical eccentricportion, said transmission rod being adapted for performing transversedisplacements with respect to the geometrical axis of the mechanicalpiece, depending on the diametral dimensions of the substantiallycylindrical eccentric portion.
 9. The apparatus according to claim 8,wherein said measuring device includes a measurement transducer fordetecting the amount of the transverse displacements of saidtransmission rod.
 10. The apparatus according to claim 9, including atubular guide casing, coupled to said second rotating, coupling element,said tubular guide casing internally housing the movable transmissionrod.
 11. The apparatus according to claim 10, including guide means forguiding the displacements of the transmission rod with respect to thetubular casing and antirotation devices for preventing the rotations ofthe transmission rod with respect to the guide casing.
 12. The apparatusaccording to claim 1, wherein the substantially Vee-shaped referencedevice is coupled to the second coupling element in a mutuallyadjustable position substantially in the direction of a bisecting lineof said substantially Vee-shaped reference device.
 13. The apparatusaccording to claim 1, wherein said substantially Vee-shaped referencedevice can be replaced for allowing variations of a measuring range ofthe measuring device.
 14. An apparatus for the diameter checking of asubstantially cylindrical eccentric portion of a mechanical piece thatdefines a geometrical axis, during eccentric rotations of said portionabout said geometrical axis in the course of machining in a numericalcontrol grinding machine with a bed, a worktable, for defining saidgeometrical axis, and a grinding wheel-slide, movable alone a directiontransverse with respect to said geometrical axis, including asubstantially Vee-shaped reference device adapted for cooperating withsaid eccentric portion to be checked, a measuring device, movable withthe substantially Vee-shaped reference device, and a support device forsupporting the substantially Vee-shaped reference device and themeasuring device, the support device including a support element, afirst rotating, coupling element coupled to the support element so as torotate about an axis of rotation parallel to said geometrical axis, asecond rotating, coupling element that carries the substantiallyVee-shaped reference device and the measuring device and is coupled tothe first coupling element so as to rotate relative to it about anadditional axis of rotation parallel to said geometrical axis and tosaid axis of rotation, limiting and reference devices, for limiting therotations of said first rotating, coupling element and said secondrotating, coupling element and for defining a rest condition of theapparatus without interfering with displacements of the substantiallyVee-shaped reference device following the substantially cylindricalportion during said eccentric rotations, a thrust device for urging saidsubstantially Vee-shaped reference device in abutment with thecylindrical eccentric portion to be checked and keeping thesubstantially Vee-shaped reference device engaged with the cylindricaleccentric portion during said eccentric rotations, the thrust devicebeing arranged between the support element and one of said first andsecond coupling elements, the abutment surfaces of said first pair andsecond pair are detached from each other during the checking of theeccentric portion, and a detecting device adapted to detect an angularposition of said substantially cylindrical eccentric portion to bechecked about said geometrical axis, the detecting device including alinear gauge providing a signal indicative of the position of the firstrotating, coupling element with respect to the support element.
 15. Theapparatus according to claim 14, wherein said detecting device includesa protruding element integral with the first rotating, coupling element,said linear gauge being fixed with respect to said support element andcomprising a feeler adapted to touch the protruding element.